Means and method for reducing cross talk in loading coils



Ami? 22 1924c 11,491,359

H. B. M. PLEIJEL. ET AL MEANS AND METHOD FOR REDUCING CROSS TALK IN LOADING COILS Filed May 5. 1921 lm e/viors Hen/1mg [3M P/ej/e/ fire/Herman 0/5071,

Patented Apr. 22, 1924.

UNITED STATES PATENT OFFICE.

HENNIN G BERNHARD MATHIAS PLEIJEL AND AXEL HERMAN 0135017, 0]? STOCKHOLM,

SWEDEN, ASSIGNORS TO WESTERN ELECTRIC COMPANY, INCORPORATED, 011' NEW YORK, N. Y., A CORPORATION OF NEW YORK.

MEANS AND METHOD FOR REDUCING CROSS TALK IN LOADING COILS.

Application filed May 5, 1921. Serial No. 467,035.

To all whom it mag concern.

Be it known that we, HENNING BERNHARD MATIIIAS PLuIJEL and Axnn HERMAN OLSON, subjects of the King of Sweden, residing at Stockholm, Sweden, have invented certain new and useful Improvements in Means and Methods for Reducin Cross Talk in Loading Coils, of which t is following is a full, clear, concise, and exact description.

This invention relates to means and methods for equalizin induction coils joined in pairs, the said induction coils servin in telephone cables to form a load of sell induction on two main lines, and simultaneously on the phantom lines formed thereof.

In the drawings, Figs. 1 to 3 are ex lanatory dia rams showin the relative irections of the magnetic elds caused by currents flowing in the various loading coil circuits; Figs. 4 and 5 show diagrammatically the testing circuits used in carrying out the equalization processes of the invention; Fig. 6 is a diagrammatic representation of the loading coil of the invention.

The arrangement of these pairs of coils is known per se from the En lish Patent No. 22,270 of 1914. In order afso to obtain a sufiicient load of self-induction for the duplex line with pairs of coils of the said character, there must be provided connecting ieces of iron at the contact places of the uplex field between the one and the other coil of the pair, so as to reduce the magnetic resistance. lhis arrangement is also known, the same having been described in the English Patent No. 22,133 of 1914. As the said connecting pieces have to be in direct contact with the cores of the coils, the winding of the cores must be interrupted at the connecting places by a space equal to the width of the connecting pieces. It has been found that for this reason and by reason of the magnetic connection of the cores of the coils by means of the connecting pieces, mutual inductive influences between the two coils are apt to cause cross talking in the said three circuits the said inductive influences being due to small unsymmetries between the magnetic paths and also between the windings of the two coils.

The removal of these unsymmetries by changing the osition of the connectin pieces and of t e windingshas been foun to be egrtremely difiicult, if not impossible. According to the invention, the pair of coils is therefore taken as it is when ready mounted, after which a compensation of the unsymmetries present is brought about only by a corresplonding equalization of the windings. T e possibility of effecting this compensation b the windings only is due to certain con itions which are necessary and suflicient for the required noniud'uctivity, the said conditions havin to he fulfilled by the co-eflicients of mutua induction between the windings of the coils, and also due to the equalizing windings arranged accordin to the invention so as to be capable of fultilling the said conditions.

In the accom )anying di'awin Fig. 1 represents. two coi s AB and A B of a pair of coils, the same being placed on top of each other although shown beside one another in the drawin The connecting pieces are assumed to e interposed between A and A and between B and B. The four halves of the windings are denoted by 1, 2, 3 and 4 their inductivities are L L L, and L The positive direction of current flow through the windingsis that which in the respective halves of the coils creates a magnetic field having a direction indicated by the arrows. By a current creating a positivel directed field in any of the halves of tie windings, there are produced, as shown by the arrows, positively directed magnetic fields in the two halves of the other coil, whereas a negatively directed produced in the second half of the first coi Thus the co-efficients of the mutual induction between the various halves of the windings are:

12 ia m 23 ae and M3A belonging together in the case of main circuit currents flowing in two coils; Fig. 3 shows them as they are m duplex operation.

In order that the two coils-of the main lines shall not influence each other, the mutual induction of the one coil in main line connection on the other coil, which is connected in the same Way, must be equal to zero. By comparing Fi 2 with Fig. 1, and assuming coil3, 4, to be inducing, it 1s found that theinductions in the halves of the coil 1, 2, must then be equal but opposite. From this second condition is derived:

The same condition will be deduced by assuming coil 1, 2, to be the inducing one.

If the main lines are not to influence the duplex line, then the induction of each coil connected as a main circuit coil on each of the two halves of the other coil have to be equal to zero, the said halves forming branches of the duplex line. hen coil 3, 4, is assumed to be an inducing main circuit coil, Fig. 2 gives the third condition:

and with coil 1, 2 as the inducing one, the fourth condition is arrived at.

Conditions 2 and 3 give together hs M28 Conditions 2 and 4 give:

M18- 14 1 M,,M

2s= From this the fifth condition 1a 14 2a 24 is obtained.

This means that the four-coefficients of mutual self-induction prevailing between the halves of the windin of adjacent coils must all equal one anot er. Conditions 1 and 5 thus represent the result obtained by the equalization.

Now, the method of equalizing is as follows: K 3

According to Fig. 1, the equations M,,=M and M =M,, of condition 5 are satisfied when the induction between coil 3, 4, in main line connection and each of the two winding halves of coil 1, 2, is equal to zero. If an alternating current for instance of a periodicity of 800 per second is sent through the coil 3, 4, in main line connection, a telephone connected to the winding half 1 or 2 of the coil'l, 2, must be silent when the conditions are fulfilled. If it is not silent, which is mostly the case, an equalization has to take place.

According to the invention, this is brought about lo aplpl ing so many windings of the win ingal ves which are being tested, or of the winding-half of the inducing coil situated beneath the same, in common around these two halves of coils, until the telephone is silent. For instance, if the Winding-half 1 is bein tion may be effected by winding a corresponding number of the windings previously Wound only on to 1, around both 1 and 3.

If the direction of winding around 3 is then the same as around 1, M will be reduced and M magnified. Conditions will be re versed 1 when the direction of windin around 3 is opposed to the direction of win ing around 1.

In the same manner, by commonly winding a suitable number of windings of half 2 tested, the.equalizaaround the halves 2 and 4, M, will be equal to M After the latter equalization the first one must be tested once more and, if necessary, be changed, so that both equalizations will at the same time fulfil the conditions made.

The next process of equalization has for its object to test condition 1, according to which L, has to be equal to L and L equal to L,,.

For this purpose each of the two coils are connected into a bridge, as shown in Fig. 4 for coil 1, 2. From the half having the larger self-inductivity, there are taken off as great a number of windings, and instead added to the half having the smaller self-inductivity, as will bring the contact G into the centre of the bridge wire. The equalization first described is not influenced by this latter equalization.

Now, the third equalization is still to be effected by which the claim M, ,=M of condition 5 is satisfied. If two circuits are formed from the four winding-halves, one of said circuits being formed by a series connection of the halves 1 and 3, while the second circuit is formed by connecting the halves 2 and 4 in series, the total inductivities of these two circuits will be 2+ 4+ 2 On account of the preceding equalization,

and

these two inductivities equal one another,

when M =M If now the air of coils is connected into a bridge as indicated in Fig. and the bridge is balanced, the contact C should be in t e centre of the bridge wire if the mutual inductances M, and M are equal to each other. If they are not equal to each other, the contact C will not be at the centre of the bridge wire, but will be located, for example, to the left of this centre, thereby indicatlng that for the particular pair of coils under test M does not equal M In order to obtain equivalence, an e ual number of windings of each of the ha ves 3 and 4, are, according to the invention, wound simultaneously for instance around the half 1. B this procedure M and M are ma nified y the same amount by which M,, an M,,, are reduced; thus the first equalization will not be changed, but it is in this way possible to bring C to the centre of the bridge wire, in order to make M,,=M,,, as re aired.

hus, the equalization of the pair of coils is completed.

In order to sim lify the equalization it is preferable to com ine only such coils into pairs in which the two halves are already made equal with respect to the inductivity, resistance and winding system. Then the second equalization procedure only comprises controlling and, if necessary, correction. The equalization can then be commenced with the correction. It is, of course, immaterial which of the two coils is treated as the first one and which is treated as the second one, when the equalization is effected.

Fig. 6 shows schematically how the corrective windings above described are inserted on the two parallel cores of the loading coil. VVindings 10 and 11 are the main line windings for the side circuit 12, 13 and 14 and 15 are the main line windings for the side circuit 16, 17. A few turns of main winding 10 are shown wound in common on core branches 18 and 19, and a few turns of main winding 11 are shown wound in common on core branches 20 and 21 for the purpose above set forth in detail. A few turns of main line windings 14 and 15 are shown Wound simultaneously around core branch 18 to further reduce cross talk between the three talking circuits. The two annular cores are suitably connected by two connecting pieces of magnetic material 23 and 24:.

Having now particularly described and ascertained the nature of our said invention and in what manner the same is to be performed, we declare that what we claim is 2-- 1. The method of reducing cross talk in a loading coil havin a core of a plurality of branches for simu taneously loading a plurality of physical circuits and a derived 7 branches an phantom circuit, which comprises removas mg a few turns of a mainline winding found on one branch of the core and rewindm said turns in common around the last mentioned branch and a second of said branches.

2. The method of reducin cross talk in a loading coil having a core 0 a lurality of branches for simultaneously loading a plurality of physical circuits and a derlved phantom clrcuit, which comprises removing a few turns of each of a plurality of main l1ne windin s found on different core winding the removed turns simultaneously upon another branch of said core.

3. A magnetic structure of a plurality of branches for simultaneously loading a plurality of physical circuits and a derived phantom circuit com risin a main line winding on one of said ranc es for each line of each physical circuit and means comprising win in s wound in common on a plurality of said ranches for reducing cross talk between said circuits.

4. A loading coil structure for simultaneously loading a plurality of physical circuits and a derived phantom clrcuit, comprising two annular cores of magnetic material, main line windings on said cores, and an auxiliary winding Wound in common on portions of both of said cores for reducing cross talk between said circuit.

5. A loading coil structure for simultaneously loading a plurality of physical circuits and a derived phantom circuit, comprising two annular cores of magnetic material, a main line winding on each half of each of said cores, and means com rising winding wound around both of sai cores in common for reducing cross talk between said circuits.

6. The method of reducing cross talk in a loading coil for simultaneously loading a plurality of physical circuits and a derived phantom circuit, said coil having a core of a plurality of branches, said core having on separate branches at least two main windings for each physical circuit, which method comprises equalizing the coefiicients of mutual induction between the main windings by winding a small number of turns of one main winding around a different branch of the core, and winding an equal number of turns from each of the two mentloned main windings of one physical circuit around a branch of the core surrounded by a main.

winding of another physical circuit.

7. A. magnetic structure of a plurality of branches for simultaneously loading a plurality of physical circuits and a derived phantom circuit comprising at least two main windings for each physical circuit located on different branches of said structure, an auxiliary winding of a small number of turns connected in circuit with one main In witness whereof, we hereunto subwinding of one physical circuit and mountscribe our names this 5th day of April, A. ed on a-branch of said structure surrounded D., 1921. by a main windin of another physical cir- 5 cuit, and a secon auxiliary winding of a HENNING BERNHARD mums P LEIJEL.

small number of turns connected in circuit AXEL HERMAN OLSON. with the second main winding of said one Bhysical circuit and mounted on the same \Vitnesses:

smell of said structure as said first auxil- OSCAR GRAHN, 10 iary winding. PETER H. BERGROTE. 

